President Obama and Mitt Romney are neck-and-neck in national polls released on the final weekend before Election Day, but Obama's Midwestern "firewall" of Iowa, Ohio and Wisconsin is holding and he maintains a distinct advantage in the contest for the 270 electoral votes needed to win the White House.

The disparity between the national and state surveys presents two potential scenarios for Tuesday night: The two will converge, with Obama edging up in the national popular vote or Romney surging in battleground states, or Obama could become the second candidate in the last four elections to win the Electoral College and the presidency while capturing fewer votes than his opponent.

The last poll from the Pew Research Center, released Sunday afternoon, swung toward Obama, giving the incumbent a slight lead, 48 percent to 45 percent. The week before, the candidates were tied, and Obama has turned around what was a 4-point deficit after the first presidential debate.

Still, the balance of the national polling shows a tied race. Those numbers largely stand in contrast to the battleground-state polling, which shows Obama with a small but perceptible advantage. He's ahead in new polls of Iowa and Ohio, while the polls diverge in Florida and show a tightening race in New Hampshire.

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In Iowa, Obama leads in the race for the state's six electoral votes, 47 percent to 42 percent, according to a Des Moines Register poll published in Sunday's editions. The poll shows Romney with a 3-point edge among men, while Obama leads by 12 points among women. More than two in five likely voters, 42 percent, have already voted, the poll found.

The race has tightened in New Hampshire, according to a new WMUR-TV Granite State Poll, which shows Obama and Romney tied at 47 percent apiece. Two weeks ago, Obama held an 8-point lead in a separate survey also conducted by the University of New Hampshire Survey Center.